The present invention relates to an unsaturated polyester resin composition and a fiber-reinforced composite material which are useful for manufacturing a molded article to which heat resistance, strength and rigidity under high temperatures are required.
In the process for mounting semiconductor components onto a printed circuit board, it is general to carry out soldering using an automatic soldering equipment. In the automatic soldering process, soldering is usually carried out by such a manner that: a printed circuit board is fixed with a fixture pallet, and the printed circuit board with the fixture pallet was automatically transported while preventing the occurrence of warp of the printed circuit board, stopped precisely at a predetermined position in the soldering equipment, and soldered in the equipment. The fixture pallet should have high rigidity enough to prevent the occurrence of warp of the printed circuit board under high temperatures at which soldering is carried out. The fixture pallets currently used have been manufactured by impregnating a heat-resistant epoxy resin onto a reinforcing glass fiber mat or the like to thereby obtain a prepreg, laminating the obtained prepregs in several layers, and then molding the resultant laminate with heat and pressure. However, this prepreg method is complicated and also disadvantageous in that the cost for production of the fixture pallet is high since the heat-resistant epoxy resins are relatively expensive. Therefore, it has been demanded to provide a fixture pallet which can be manufactured at lower cost and has excellent heat resistance.
On the other hand, for the purpose of surely preventing the occurrence of warp of the printed circuit board, reinforcing rods (stiffeners) are usually mounted onto the fixture pallet. The stiffener is required to have satisfactory-heat resistance and high strength, and therefore, duralumin-type aluminum alloys or titanium alloys have been used for the stiflenet. However, the coefficient of linear thermal expansion required for the fixture pallet is 7.0 to 8.0.times.10.sup.-6 [1/.degree.C. ], whereas, for example, that of an aluminum alloy is much larger as high as 24.times.10.sup.-6 [1/.degree.C. ]. Accordingly, if the above fixture pallet is repeatedly used in the automatic soldering process, the screw clamp between the fixture pallet and the stiffener is likely to remove by the influence of the thermal expansion hysteresis which may undergo during the soldering process, which is unfavorable.
For solving the above problem, it has been attempted to use the same material for the stiffener as that for the fixture pallet. For example, a stiffener is manufactured by cutting a laminate comprising an epoxy resin having heat resistance and glass fiber cloths into an suitable size. However, this method is not practically advantageous, since the laminate itself is expensive and the cost for cutting the laminate is additionally needed. As the method for manufacturing a stiffener at relatively low cost, a pultrusion molding method has been proposed. However, this method also has problems that, in the case where an epoxy resin or a phenol resin is used, it is difficult to carry out pultrusion, and that, in the case where an unsaturated polyester resin is used, the deterioration in physical properties of the resultant molded article, such as strength and rigidity, may occur during the soldering process under high temperatures.
As mentioned above, a stiffener for fixture pallet, which can be manufactured at low cost and has excellent heat resistance, has not been developed yet. Therefore, there has been strongly demanded a novel resin for pultrusion, which can provide a molded article having desired characteristics.
As the current methods for manufacturing a molded article excellent in strength and rigidity under high temperatures using an unsaturated polyester resin, there are mentioned, for example, methods which are respectively characterized in: (1) that the amount ratio of the unsaturated dibasic acid in the acid component is increased; (2) that isophthalic acid or terephthalic acid is used as the saturated dibasic acid; and (3) a polyfunctional monomer, such as divinyl benzene and triallyl isocyanurate, is incorporated as the diluent monomer. In addition, there have been disclosed an unsaturated polyester resin which is produced using 2-methyl-1,3-propanediol as the polyhydric alcohol component in an amount of 5 to 10 mol % based on the total amount of the entire glycol components (Japanese Patent Application laid-open Nos. Sho 48-25090, Hei 3-24122 and Hei 4-88052) and an unsaturated polyester resin which is produced using cyclohexane dimethanol as the polyhydric alcohol component (Japanese Patent Publication No. Sho 52-48158), which resins are proposed for the purpose of improving heat resistance, water resistance and hardness of the unsaturated polyester resins. However, even if any one of the above resins is used, the resultant molded article having satisfactory strength and rigidity under high temperatures has not been obtained yet.